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The recent sunscreen guidance issued by the US FDA prohibited the use of SPF ratings on hair-care products, even though these products may contain photoprotective ingredients listed on the sunscreen monograph. The US FDA has also questioned the adequacy of photoprotection provided by spray on sunscreens. These concerns are understandable based on the discontinuous film created by spray on products. It is estimated in clinical testing that the SPF on the packaging can only be achieved if the spray sunscreen is applied following by rubbing three consecutive times. While this is possible on skin, it is not possible on hair. Spray sunscreens for the hair cannot possibly evenly coat every square inch of the hair shaft. It also doubtful how much sun protection is provided by shampoos and rinse away instant conditioners that contain sunscreen. The short contact time followed by abundant water rinsing may remove any photoprotection. This then begs the question as to whether nonliving hair shafts really need sun protection at all. The answer is most emphatically “yes,” and I will proceed to explain this important cosmetic need.

As hair is nonliving, it cannot be sunburned or undergo photocarcinogenesis; however, UV and visible radiation are very damaging to the cosmetic value of the hair. Much of the current understanding of hair photodamage comes from textile research on wool. Natural fibers, such as wool, cotton, silk, and rayon, discolor when exposed to sunlight. White fabrics tend to take on a light brown/yellow color, a process known as photoyellowing. In natural human hair, there are two pigments, eumelanin and pheomelanin, accounting for the brown and red hues seen in hair, respectively. There is another melanin, known as oxymelanin, found in unprocessed human hair that has been exposed to sunlight. Oxymelanin is an oxidative photodegradation product.[1]

Lighter-colored hair, such as blonde hair, is more susceptible to hair photodamage than deeply pigmented hair, such as brown hair. Black hair begins to lighten in color after 300 h of exposure to simulated sunlight, while blonde hair begins to yellow after 300 h of exposure to simulated sunlight and begins to lighten when exposed to 300–1200 h of simulated sunlight exposure. The hair color lightening or bleaching is primarily due to the effects of visible light. However, not only does the hair change color, but it also experiences a 200–300% increase in friction, indicating damage to the proteins in the cuticle.

The hair protein that is mainly damaged by sunlight is cystine, which is oxidized to cysteic acid. It is the sulfur-containing amino acids that are most sensitive to oxidative damage, and of course, it is the sulfur-containing amino acids that give the hair its structural strength. Other amino acids, such as tryptophan and tyrosine, are also degraded by light. After 150 h of sun exposure, blonde hair shows a 25–30% decrease in tryptophan, 25% decrease in cystine, and 80% decrease in tyrosine. As oxidation occurs, there is a compensatory 80% increase in cysteic acid. These same changes are also seen in black hair, but at least 300 h of sun exposure was required to produce the same oxidative damage.[2]

Sunlight also decreases the tensile strength of the hair fiber. This means that when the hair is combed and stretched, it is more likely to break. This effect is magnified with age as the diameter of the hair shaft decreases in both men and women. The diameter of female hair shaft increases up to age 35 and then decreased gradually after age 40 with further decreases after menopause. In men, the diameter of the hair shaft decreases after puberty.

The natural photoprotection in hair is melanin, which also provides endogenous photoprotection in the skin. Melanin is broken down by visible and UV radiation in the hair shaft giving rise to a phenomenon known as photobleaching. This phenomenon is especially pronounced in blonde hair, which lightens dramatically in the summer, but also results in permanent changes in the hair shaft internal amino acids and external lipids.

Unpigmented hair, such as gray and white hair, is more susceptible to UV damage than pigmented hair.[3] Also, the rate of cystine disulfide bond breakage is greater for unpigmented than pigmented hair. This means that one of the best sources of photoprotection is hair dye.

White unpigmented hair looses more mechanical strength after 4 days of UV radiation than semipermanently dyed brown hair. This same effect is also present with permanent hair dyes. The permanent hair dye acts as a passive photofilter reducing the hair fiber protein damage by attenuating the incident light. The dye molecule absorbs the light energy, which promotes it to a more excited stated, followed by a return to ground state via radiative and nonradiative pathways. As might be expected, the darker the hair color the more photoprotection imparted by the dye.

SPF rated sunscreens to promote hair beauty and health probably will not be forthcoming in light of the new sunscreen guidance. Indeed, consumers might misinterpret sunscreen-containing hair products and mistakenly think that if the shampoo runs over the body, adequate sunscreen might be left behind. Yet, there is a need within current regulation to address the fact that sun exposure is detrimental to hair beauty. Consumers seem much more pre-occupied with having a “good hair day” than wearing sunscreen on their face and bodies to insure a “good skin day”. Perhaps cross-education from sunscreen-containing hair-care products might spill over into proper skin sunscreen application, especially in impressionable adolescents. It is also worthwhile to give consumers an idea of how much photoprotection they are getting from hair-care products to maintain hair beauty. With new sunscreen technology, it may be time to create a separate hair sun protection scale to make consumers aware of how to more effectively beautify their hair. Who knows, it might be enough to encourage a renewed interest in skin photoprotection!

References

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  2. References
  • 1
    Hoting E, Zimmerman M. Sunlight-induced modifications in bleached, permed, or dyed human hair. J Soc Cosmet Chem 1997; 48: 7991.
  • 2
    Gonzenbach H, Johncock W, De Polo KF et al. UV damage on human hair. Cosmet Toilet 1998; 113: 439.
  • 3
    Tolgyesi E. Weathering of hair. Cosmet Toilet 1983; 98: 2933.